Vehicles may include various actuators that operate using a source of vacuum. The vacuum actuators may be used for actuation, enabling vehicle brakes, purging a fuel canister, improving an engine start, performing a leak test, etc. Accordingly, various vacuum sources may be available on the vehicle. These may include dedicated vacuum pumps as well as vacuum generating ejectors, aspirators, and venturis. Engine control systems may harness an air flow through the ejector/aspirator/venturi to produce a vacuum which is then used for the various actuators.
One example approach for directing a flow through an ejector to generate vacuum is shown by Suzuki et al. in US2008/0103667. Therein, an air ejector is coupled in a surge tank upstream of a branched intake manifold having air intake throttles in each branch. A mixture of intake air and crankcase gases flowing to the intake manifold is used as motive flow to create vacuum at the ejector, the vacuum then directed to a brake booster. A ratio of intake air relative to PCV gas directed through the ejector is controlled by a negative pressure regulating valve upstream of the ejector. In particular, air is combined with the crankcase gases in the closed crankcase ventilation system to amplify the intake vacuum generated for brake boosting.
However the inventors herein have identified potential issues with such an approach. As one example, the configuration of Suzuki et al. relies on PCV flow in a direction from the intake manifold to the crankcase to generate vacuum at the ejector. However, during selected engine operating conditions, such as during engine idling conditions in an open crankcase ventilation system, PCV flow may not be in the direction relied upon, but rather in an opposite direction from the crankcase to the intake manifold. As another example, the air flow rate through the ejector required to generate sufficient vacuum flow rate may interfere with the minimum controllable air flow budget due to more air flowing than the engine needs. In addition, the required air flow rate can also interfere with air-fuel ratio control. Further still, the system of Suzuki requires complex co-ordination between the negative pressure regulating valve and the throttle valves of the intake manifold to enable engine air control.
In one example, some of the above issues may be addressed by a method of operating an engine comprising flowing gasses, in both directions, through a positive crankcase ventilation (PCV) line, between an intake manifold and a crankcase via a variable venturi to generate vacuum at the venturi. In this way, irrespective of the direction of flow through the PCV line, vacuum may be generated for subsequent use.
For example, one or more aspirators, ejectors, and/or variable venturis may be positioned between an engine intake manifold and a crankcase, in a PCV line. Based on the direction of flow in the PCV line between the intake manifold and the crankcase, air and/or crankcase gases may be directed through an aspirator, and a vacuum may be generated at the aspirator. For example, during conditions when intake manifold pressure (MAP) is higher than barometric pressure (BP), air may flow through the PCV line from the intake manifold to the crankcase via a first (e.g., bi-directional) aspirator. Then, during conditions when MAP is lower than BP, crankcase gases may flow through the PCV line from the crankcase to the intake manifold via a second (e.g., uni-directional) aspirator. In addition, some crankcase gases may flow via the first, bi-directional aspirator. Thus during both directions of flow through the PCV line, the flow of air or crankcase gases via the venturi generates a vacuum that is drawn into and stored in a vacuum reservoir. In one example, the uni-directional aspirator may be a variable throat area venturi and a flow rate of crankcase gases through the venturi can be adjusted by adjusting a throat area of the venturi.
In this way, by enabling flow of intake air and/or crankcase gases through a venturi/aspirator/ejector irrespective of the direction of flow through a PCV line, flow during both boosted and un-boosted engine conditions can be advantageously used to generate vacuum. In other words, a much broader window for vacuum generation is enabled, and engine vacuum generation efficiency is improved. By enabling vacuum generation to be enabled at a wider range of airflow rates, the minimum controllable airflow budget of the engine is not affected. Likewise, engine air-fuel ratio control is also not affected. By improving vacuum generation from PCV flow during idle engine conditions, idle air flow rate control is also improved. In addition, a rate of PCV flow through a crankcase oil separator can be maintained substantially constant, thereby improving PCV flow oil separation.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.